(a) Field of the Invention
The present invention relates to a hardenable composition, an aqueous gel and applications of said gel, and particularly to a hardenable composition, an aqueous gel, a thermosensitive plate-shaped composite material, a fire-resistant plate-shaped composite material, a water-absorbable composition and processes for producing them.
More particularly, the present invention relates to a hardenable composition comprising (meth)acrylamide or (meth)acrylamide derivative(s), particulate metal oxide(s) and an aqueous medium; an aqueous gel obtained by curing said composition and a process for producing the gel; a thermosensitive plate-shaped composite material and a fire-resistant plate-shaped composite material both comprising two or more transparent plates and an aqueous gel interposed between them, and processes for producing the composite materials; and a water-absorbable composition.
(b) Description of the Prior Art
It has been attempted to use aqueous gels to various applications for their water-holding ability. However, the applications have been virtually limited mostly to a sanitary field and the applications to other fields have been insufficient. Various reasons are considered for that. For example, when it is aimed to apply an aqueous gel as a fire-resistant material in view of the non-flammability and fire extinguishability of water, the gel has no sufficient flame resistance; accordingly, the actual use of aqueous gel as such a material is not realized. Also when it is aimed to apply an aqueous gel as a water-absorbable material (e.g. water-stopping agent), the gel itself has no elasticity and is fragile; therefore, the use of aqueous gel to such an application is limited to special fields.
In order to improve the above situation, various attempts were made. With respect to the fire-resistant material, Japanese Patent Publication No. 24063/1985 proposed a fire-resistant glass comprising glass plates and an aqueous gel consisting of a polymer of an acrylic acid derivative and a water-soluble silicate (e.g. soluble glass), interposed between the glass plates.
The aqueous gel can exhibit an intended fire-resistant property in a required thickness; however, the thickness must be large because the fire resistance of the aqueous gel is exhibited by the water boiling caused by heating and consequent foaming of gel. This large thickness poses a big restriction when the aqueous gel is used for applications other than fire wall.
Further, the above aqueous gel uses a water-soluble silicate and is strongly alkaline; hence, for example, when the glass plates are broken, there occurs the leakage of a strongly alkaline substance, bringing about a highly dangerous state. Moreover, the strongly alkaline substance acts on the polymer of an acrylamide derivative which is a constituent of the gel, causing the deterioration of the polymer.
Japanese Patent Application Kokai (Laid-Open) No. 91446/1987 proposed addition of a corrosion-resistant substance to a water-soluble salt. Japanese Patent Application Kokai (Laid-Open) No. 264942/1989 proposed combined use of a polyvinyl alcohol gel and a water-soluble salt. These approaches, however, provide no sufficient fire resistance. Further, in the latter approach, the operation of sealing a low-fluidity gel in between glass plates poses a big problem in production of fire resistant material.
Further, there were developed various aqueous gels of high elasticity, for example, a gel of a vinyl alcohol/acrylic acid copolymer which is a saponification product between methyl acrylate and vinyl acetate and a gel of an isobutylene-maleic anhydride copolymer. These aqueous gels of high elasticity, however, give no sufficient results.
There is known, in U.S. Pat. No. 4,828,710, a resin for adsorption of water or useful substances, consisting of a polymer of an N-alkyl or N-alkylene-substituted (meth)acrylamide or a copolymer of said monomer with other monomer copolymerizable therewith. There is also known a material comprising a carrier (e.g. silica) and the above resin supported thereon.
Further, it is known in European Patent No. 406432 that a spherical (bead-like) polymer obtained by polymerizing the above-mentioned monomer in a concentrated aqueous inorganic salt solution containing fine inorganic particles in a suspended form and then precipitating the resulting polymer by salting out, is useful for concentration of easily degrading substances (e.g. amino acids, proteins) or as a substrate capable of slowly releasing mediciens, etc.